Emissitivity of copper - Why are copper heatsinks all shiny? This wikipedia article states that emissivity of polished copper is 0.04, and emissivity of oxidized copper is 0.87 - more than 20x of the polished copper.
So my question is - why are all copper heatsinks shiny and polished?
Wouldn't oxidized copper heatsink be much more effective in radiating the heat away from the source?
Searching for "oxidized copper heatsink" I find people asking and giving advice on how to remove oxidation from the heatsink because it makes the heatsink less effective - seemingly contradicting the information presented on given wikipedia article?
Is there something I am misunderstanding about emissive properties of a material?
Is there a way I could oxidize a copper heatsink in order to make it more effective?
 A: Radiative heat transfer is not dominant at the temperatures at which computer/electronic heatsinks operate, so the emissivity of the heatsink fin surfaces is not important for their operation. 
Conduction of heat from the copper to the air, and then convection driven either by buoyancy or mechanical ventilation, is the dominant heat transfer mode that heatsinks exploit. 
This makes the cleanliness of the fins far more important than their emissivity, which means anything that maintains them in a dust-free state will enhance their operation. This is why heatsink fins are made as smooth as possible, and not rough, and why the fan intake will have a lint filter on it. 
The oxide tarnish that naturally forms on exposed copper fins at near-room temperatures is far thinner than a thousandth of an inch and therefore has a negligible effect on heat transfer. People who polish the oxides off to "improve" heat transfer are misinformed.
A: Although you make a good argument for the efficiency of emissivity (radiation), it seems you forgot about conduction and convection.
In the environment and the temperature surrounding electronic circuits, conduction and convection, are the dominant means of heat transfer.  To maximize these methods, a clean and smooth surface is required between the hot object and its heat-sink, as well as between the heat-sink and the fluid flowing between its fins.  
Although maximizing the conduction efficiency reduces the radiation efficiency, the gain in conduction more than offsets the reduction.   
A: the purpose of a heatsink is to conduct heat, to transfer it, away from a component as fast as possible, to a radiator(where emissivity is more important) that is usually made of anodized Aluminum(better emissivity & convection properties than rusty copper).  
